Re: [PATCH v2] [gdb/testsuite] Fix timeout in gdb.base/bg-execution-repeat.exp

[Guinevere Larsen <blarsen@redhat.com>]

On 6/20/24 8:56 AM, Tom de Vries wrote:
> I ran into the following test failure with test-case
> gdb.base/bg-execution-repeat.exp:
> ...
> (gdb) PASS: gdb.base/bg-execution-repeat.exp: c&: repeat bg command
> ^M
> Breakpoint 2, foo () at bg-execution-repeat.c:23^M
> 23        return 0; /* set break here */^M
> print 1^M
> $1 = 1^M
> (gdb) PASS: gdb.base/bg-execution-repeat.exp: c&: input still accepted
> FAIL: gdb.base/bg-execution-repeat.exp: c&: breakpoint hit 2 (timeout)
> ...
>
> The failure can be easily reproduced by adding a sleep 5 here:
> ...
> +    sleep 5
>       gdb_test "print 1" " = 1" "input still accepted"
> ...
>
> There's a race in the test-case, between:
> - the command handled in the foreground: the "print 1" command, and
> - the command handled in the background: the continue command.
>
> The current way of dealing with this is by putting the inferior to sleep for 5
> seconds:
> ...
>    foo ();
>    sleep (5);
>    foo ();
> ...
> with the aim that the "print 1" command will win the race.
>
> This method is both slow and unreliable.
>
> Fix this by making the inferior wait till the "print 1" command is done.
>
> This reduces running time from ~11s to ~1s.
>
> I also verified that the test-case still triggers on the original problem by
> applying this gdb/infcmd.c patch:
> ...
> -strip_bg_char (const char *args, int *bg_char_p)
> +strip_bg_char (const char *_args, int *bg_char_p)
>   {
> -  const char *p;
> +  char *args = const_cast<char *>(_args);
> +  char *p;
>
>     if (args == nullptr || *args == '\0')
>       {
> @@ -210,6 +211,7 @@ strip_bg_char (const char *args, int *bg_char_p)
>         p--;
>         while (p > args && isspace (p[-1]))
>   	p--;
> +      *p = '\0';
> ...
>
> Tested on x86_64-linux, with make-check-all.sh.
>
> PR testsuite/31794
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31794
> ---
>   gdb/testsuite/gdb.base/bg-execution-repeat.c   | 18 +++++++++++++++++-
>   gdb/testsuite/gdb.base/bg-execution-repeat.exp |  9 +++++++++
>   2 files changed, 26 insertions(+), 1 deletion(-)
>
> diff --git a/gdb/testsuite/gdb.base/bg-execution-repeat.c b/gdb/testsuite/gdb.base/bg-execution-repeat.c
> index 2caa7d442f6..d5b48ee4f94 100644
> --- a/gdb/testsuite/gdb.base/bg-execution-repeat.c
> +++ b/gdb/testsuite/gdb.base/bg-execution-repeat.c
> @@ -23,11 +23,27 @@ foo (void)
>     return 0; /* set break here */
>   }
>   
> +static volatile int do_wait;
> +
> +static void
> +wait (void)
> +{
> +  while (do_wait)
> +    usleep (10 * 1000);
> +}
> +
>   int
>   main (void)
>   {
> +  alarm (60);
> +
>     foo ();
> -  sleep (5);
> +
> +  do_wait = 1;
> +  wait ();
> +  /* do_wait set to 0 externally.  */
> +
>     foo ();
> +
>     return 0;
>   }
> diff --git a/gdb/testsuite/gdb.base/bg-execution-repeat.exp b/gdb/testsuite/gdb.base/bg-execution-repeat.exp
> index a4cc7daa702..35ddb34cd8f 100644
> --- a/gdb/testsuite/gdb.base/bg-execution-repeat.exp
> +++ b/gdb/testsuite/gdb.base/bg-execution-repeat.exp
> @@ -68,6 +68,15 @@ proc test {continue_cmd} {
>       # stopped.
>       gdb_test "print 1" " = 1" "input still accepted"
>   
> +    # With gdbserver, we cannot set memory while the inferior is running, so
> +    # enable the "set var" command with an interrupt / continue& pair.
> +    gdb_test -no-prompt-anchor "interrupt"
> +
> +    # Allow the breakpoint to trigger.
> +    gdb_test -no-prompt-anchor "set var do_wait=0"
> +
> +    gdb_test -no-prompt-anchor "continue&"
> +
>       # Make sure we see a stop after the print, and not before.  Don't
>       # expect a prompt, as we had resumed the inferior in the background.
>       set test "breakpoint hit 2"
>
> base-commit: b5929e7aa0195a0656a63da95d5eccbb73b5b173

Thanks for this, I always like when we can make tests run faster. Testes 
with unix, native-gdbserver and native-extended-gdbserver with both gcc 
and clang.

Just a suggestion, on line 45 there is a use of gdb_test_multiple with a 
prompt with no anchor. It seems to me that that test could be 
substituted for `gdb_test -no-prompt-anchor` too.

Either way, this patch is a good change, Reviewed-By: Guinevere Larsen 
<blarsen@redhat.com>

-- 
Cheers,
Guinevere Larsen
She/Her/Hers